Issue |
A&A
Volume 435, Number 2, May IV 2005
|
|
---|---|---|
Page(s) | 563 - 574 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20042235 | |
Published online | 29 April 2005 |
The mid-IR spatially resolved environment of OH 26.5+0.6 at maximum luminosity
1
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: chesneau@mpia-hd.mpg.de
2
Insituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
3
Observatoire de la Côte d'Azur-CNRS-UMR 6203, Boulevard de l'Observatoire, BP 4229, 06304 Nice Cedex 4, France
4
Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
5
Sterrewacht Leiden, Niels-Bohr-Weg 2, 2300 RA Leiden, The Netherlands
Received:
22
October
2004
Accepted:
12
January
2005
We present observations of the famous OH/IR star
OH 26.5+0.6 obtained using the Mid-Infrared Interferometric Instrument
MIDI at the European Southern Observatory (ESO) Very Large Telescope
Interferometer VLTI. Emission of the dusty envelope, spectrally
dispersed at a resolution of 30 from 8 μm to 13.5 μm, appears
resolved by a single dish UT telescope. In particular the angular
diameter increases strongly within the silicate absorption band.
Moreover an acquisition image taken at 8.7 μm exhibits, after
deconvolution, a strong asymmetry. The axis ratio is with
the FWHM of the major and minor axis which are 286 mas and 214 mas
respectively. The measured PA angle, 95
, is
reminiscent of the asymmetry in the OH maser emission detected at
1612 MHz. In interferometric
mode the UT1-UT3 102 m baseline was employed to detect the presence of
the star. No fringes were found with a detection threshold
estimated to be about 1% of the total flux of the source,
i.e. 5-8 Jy. These observations were carried out during the
maximum luminosity phase of the star, when the dust shell is more diluted and
therefore the chance to detect the central source maximized. We modeled
the dusty environment based on the work of Justtanont et al. (1996). In
particular, the failure to detect fringes provides strong constraints
on the opacities in the inner regions of the dust shell or in the
close vicinity of the star.
Key words: radiative transfer / techniques: interferometric / stars: AGB and post-AGB / stars: circumstellar matter / stars: individual: OH 26.5+0.6
© ESO, 2005
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